Change the backspace key default about mintty HOT 8 CLOSED

I assume you found the backspace key code setting on the "Keys" pane. I'd 
almost made
^? the default because it clearly is The Right Way™ but I chickened out 
because ^H is
the default in all the other terminals in Cygwin and I didn't want to risk
incompatibilities with Cygwin programs.

The backspace keycode default is being changed to ^? in Cygwin 1.7, so when (or 
if?)
the xterm terminfo entry for backspace is changed, the default it MinTTY can 
change
as well.

In fact I might just remove the backspace keycode option altogether, and instead
implement the DECBKM control sequence in case anyone still wants to change it 
back to ^H.

Might as well remove the escape keycode option too and replace it with a private
control sequence, as it's probably just puzzling rather than useful for most 
users.

Done in r444 on trunk.

Could we please, please put the option for ^H back.

I administer have literally thousands of servers that expect ^H to be the 
backspace
key (wrong, of course, but that it is the way it was set up and there is no 
changing
that wrongness now).  Logging on and having to type stty each time I come from 
cygwin
is a poor solution.

Go ahead and set the default to ^?, but put the option to set it back to ^H in. 
There is a reason that putty and everyone else has this setting.

There's the DECBKM sequence as a replacement for the option:

echo $'\e[?67h'

Reinstated backspace keycode option for 0.5.2 after all, to try and avoid 
further
grief with this godawful issue.